1. Field of the Invention
The present invention relates to a process for preparing a patterned organic layer from an unpatterned water-soluble organic layer. More particularly, the present invention relates to an improved for fabricating an electronic device having a patterned organic layer adjacent to an organic semiconducting material, metal or insulator layer.
2. Description of the Prior Art
A number of materials used in organic electronic and optoelectronic devices are degraded by exposure to organic solvents such as those used in photolithographic processing. For example, pentacene-based organic thin film transistors have demonstrated performance comparable to, or better than, devices fabricated using hydrogenated amorphous silicon active layers (D. J. Gundlach, H. Klauk, C. D. Sheraw, C. C. Kuo, J. R. Huang, and T. N. Jackson, xe2x80x9cHigh-Mobility, Low Voltage Organic Thin Film Transistors.xe2x80x9d 1999 International Electron Devices Meeting Technical Digest, pp. 111-114, December 1999 and H. Klauk, D. J. Gundlach, J. A. Nichols, and T. N. Jackson, xe2x80x9cPentacene Organic Thin Film Transistors for Circuit and Display Applications,xe2x80x9d IEEE Transactions on Electron Devices, Vol. 46, No. 6., pp. 1258-1263, June 1999).
However, when deposited by vacuum evaporation, pentacene thin films typically grow in a thin film phase with an elongated c-axis compared to bulk crystals. Exposure to some organic solvents (isopropyl alcohol or acetone, for example) results in a solvent-induced phase transition to the bulk phase with an associated in-plane expansion (see, for example, D. J. Gundlach, T. N. Jackson, D. G. Schlom, and S. F. Nelson, xe2x80x9cSolvent-Induced Phase Transition in Thermally Evaporated Pentacene Films,xe2x80x9d Applied Physics Letters, Vol. 74, No. 22, pp. 3302-3304, May 1999).
Such solvent-induced in-plane expansion results in buckling of the thin film and degraded device properties. FIG. 1 shows an atomic force microscope image of pentacene thin film before exposure to isopropyl alcohol. FIG. 2 shows an atomic force microscope image of pentacene thin film after exposure to isopropyl alcohol. The image in FIG. 2 shows film buckling (note the change in the vertical scale).
Similar organic solvent related degradation is also observed for devices fabricated with -sexithienyl or napthacene and for many other organic materials used for organic electronic and optoelectronic devices including organic thin film transistors and organic light emitting diodes. This degradation is problematic since it makes it difficult to do conventional photolithography on organic materials or with organic materials present.
The present invention provides an aqueous-based photolithographic process for preparing a patterned organic layer from an unpatterned water-soluble organic layer. This process uses water as both the solvent for the photosensitive material for solvent-casting in thin film form and for developing the image after exposure. As a result, the process of the present invention avoids the problems associated with organic solvents based conventional photolithography, such as, solvent-induced in-plane expansion, which results in buckling of the thin film and degraded device properties.
The present invention provides a process for preparing a patterned organic layer from an unpatterned water-soluble organic layer. The process includes the steps of:
imagewise exposing to radiation a photosensitive unpatterned water-soluble organic layer deposited on an organic semiconducting material, a metal or an insulator layer, to produce to produce an imagewise exposed organic layer having exposed and unexposed regions; and
contacting the imagewise exposed organic layer and an aqueous-based developer to selectively remove the unexposed regions thereby producing the patterned organic layer.
The present invention further includes a process for preparing a patterned organic transistor layer on a transistor structure. This process includes the steps of:
applying onto an unpatterned organic transistor layer disposed on a transistor structure an aqueous solution including a photosensitive composition to produce an unpatterned photosensitive organic layer;
imagewise exposing the unpatterned photosensitive organic layer to radiation to produce an imagewise exposed organic layer having exposed and unexposed regions; and
contacting the imagewise exposed organic layer and an aqueous-based developer to selectively remove the unexposed regions thereby producing a patterned organic layer on the unpatterned organic transistor layer.
The present invention still further includes a process for preparing a patterned organic diode layer on a diode structure. This process includes the steps of:
applying onto an unpatterned organic diode layer disposed on a diode structure an aqueous solution including a photosensitive composition to produce an unpatterned photosensitive organic layer;
imagewise exposing the unpatterned photosensitive organic layer to radiation to produce an imagewise exposed organic layer having exposed and unexposed regions; and
contacting the imagewise exposed organic layer and an aqueous-based developer to selectively remove the unexposed regions thereby producing a patterned organic diode layer on the unpatterned organic diode layer.
Also provided is an improved process for fabricating an electronic device having a patterned organic layer adjacent to an organic semiconducting material, metal or insulator layer. The improvement includes the steps of:
imagewise exposing to radiation a photosensitive unpatterned water-soluble organic layer deposited on an organic semiconductor material, a metal or an insulator layer in the electronic device to produce an imagewise exposed organic layer having exposed and unexposed regions; and
contacting the imagewise exposed organic layer and an aqueous-based developer to selectively remove the unexposed regions.
The present invention also includes the products prepared by any of the above processes.
The process of the present invention avoids the problems associated with organic solvents based conventional photolithography in which the organic solvents are used either as solvents for the photosensitive material or as a component of the developer.